The invention relates to an apparatus for guiding X-rays from a radiation source to a measurement object.
The X-ray fluorescence method is used for measuring thin layers or multilayers. In the course of layer analysis of this type, the X-ray fluorescent radiation of the individual elements of a sample is detected and converted into layer thickness(es) and composition(s). Masked by a collimator system, the exciting X-rays pass in the form of a fine beam of rays to the measurement area. From here, the X-ray fluorescent radiation is emitted. The radiation is detected in an energy-dispersive manner in a proportional counter tube or another detector. Functional areas having dimensions up to a size of 100 xcexcmxc3x97100 xcexcm, for example, can be determined exactly in a contactless and non-destructive manner by means of a layer thickness analysis of this type.
For the layer thickness analysis of smaller functional areas of less than 100 xcexcmxc3x97100 xcexcm, for example, X-ray conductors are known which enable the X-rays to be focussed onto these small functional areas. They are what are called monocapillaries. These monocapillaries are designed cylindrically in the form of a small glass tube. Total reflection at the walls of the glass tube enables the X-rays to be guided with sufficient intensity to the measurement object.
Furthermore, the collimators designed as monocapillaries have been developed further to the effect that the internal walls of the glass tubes are of parabolic design, so that the reflected rays are intended to be focussed towards the measurement object. Moreover, so-called polycapillaries are known. These are a monolith which has a bundle of a plurality of monocapillaries, the latter in turn being arranged in such a way that the X-rays which are guided in a targeted manner are focussed at a point outside the exit plane of the monolith.
These capillaries have the disadvantage that they are expensive and layer-thickness measuring devices with these collimators cannot be produced economically. Moreover, the above-described collimators have the disadvantage that their diameter is fixed, so that there is no possibility for adjusting and focussing the X-rays to a different size of the measurement object. Furthermore, these collimators have the disadvantage that procurement is made extremely difficult since the production of these collimators is monopolized in particular on account of their complexity.
The invention is based on the object, therefore, of providing an apparatus for guiding the X-rays from a radiation source to a measurement object, in particular for small structure sizes having a functional area of less than 100 xcexcmxc3x97100 xcexcm, which can be produced cost-effectively, can be adjusted to the measurement area to be measured, and enables sufficient transmission of the radiation intensity to the measurement object.
This object is achieved according to the invention by means of an apparatus in accordance with claim 1.
The invention""s configuration of at least two reflecting areas forming a slit has the advantage that a simple arrangement has been created which enables the X-rays to be guided with sufficient intensity to the measurement object, in order to enable the detector to detect a sufficient intensity of the fluorescent radiation emitted. The at least two reflecting areas forming a slit are simple to produce. In comparison with the mono- and/or polycapillaries known from the prior art, manufacturing methods for producing the apparatus for guiding X-rays are not complicated.
In contrast to the prior art, in which the mono- or polycapillaries are formed from completely closed small glass tubes, it suffices according to the subject-matter of the invention for the X-rays to be guided to the measurement object by total reflection within a slit formed by at least two reflecting areas. The X-rays emerging laterally from the slit or slits are ineffective for the excitation of the fluorescent radiation, but an at least sufficient intensity is conveyed or transferred to the measurement object by the total reflection of the X-rays between the at least two reflecting areas forming a slit.
One advantageous embodiment of the invention provides for the slit formed by the at least two reflecting areas to have an adjustable width. This enables the size of the measurement area on the measurement object to be adjustable. Consequently, the apparatus can be adjusted and adapted to different requirements of the layer thickness analysis.
One advantageous embodiment of the invention provides for two reflecting areas to be provided which are opposite one another and are arranged parallel to one another. This can provide a structurally simple configuration for guiding X-rays. The slit width is adapted at least to the size of the measurement area of the measurement objects and advantageously to the exit opening of the X-ray tube, so that a maximum radiation intensity can be transferred to the measurement object.
An alternative embodiment of the invention provides for two reflecting areas to be provided which are opposite one another and have a slit which tapers towards the measurement object. Additional focussing of the X-rays can be obtained by virtue of this approximately wedge-shaped arrangement of the reflecting areas. The aperture width of the reflecting areas between the input and the output provided at the tapering end may be in the micrometer range or larger;
A further advantageous embodiment of the invention provides for at least one reflecting area to be fixed and at least one further reflecting area to be adjustable in terms of distance and/or angle. This means that optionally either distance and/or angle can be adjusted in a manner dependent on the application, one reflecting area serving as a reference area.
A further advantageous embodiment of the invention provides for the reflecting areas to be produced from a semiconductor material, in particular from a silicon wafer. Industrial production of the silicon wafers has become cost-effective in the mean time. Moreover, on account of the highly planar configuration, the silicon wafers have a surface which is suitable for the total reflection of the X-rays. The critical angle of total reflection is a few mrad, for example, depending on the energy of the X-rays. The rays can be forwarded in a manner sufficiently free of losses by virtue of the high-quality planar surface of the silicon wafers.
It is advantageously provided that the reflecting areas at least partly have vapour-deposited on them a noble metal, preferably copper, silver, gold, platinum, palladium or the like. By virtue of this coating, which is preferably provided on a silicon wafer, the critical angle can be increased to 4.5 mrad, for example in the case of a platinum coating, as a result of which the critical angle for total reflection can be increased. This in turn leads to the effect whereby there is a higher intensity of the X-rays at the measurement object, which means that it is possible to provide a sufficiently high intensity for emitting fluorescent rays.
A further advantageous embodiment of the invention provides for the coating to be provided at least partly at an end facing the beam exit of the X-ray tube. This enables a multiplicity of X-rays to be reflected by total reflection in the input region, as a result of which a high intensity can be obtained.
A further advantageous embodiment of the invention provides for the reflecting areas to have near the measurement object a region which has a coating that prevents total reflection, or, in the case of at least partly coated reflecting areas, has a region which is provided without a coating or in which a coating that prevents total reflection is provided.
This means that it becomes possible to eliminate the total reflection of rays which would lie outside the measurement region after a final reflection prior to exit from the reflecting areas. This arrangement makes it possible to obtain even more exact irradiation of the measurement area at a measurement object, which in turn increases the measurement quality.
One advantageous embodiment of the invention provides for at least one reflecting area to be adjustable by at least one adjusting unit. This adjusting unit may advantageously be designed as precision mechanical adjustment or as an electrical, hydraulic, pneumatic or piezo-electronic actuator. This adjusting unit must enable adjustments at least in the micrometer range in order to afford exact orientation and adjustment of the at least two reflecting areas which are arranged relative to one another.
Further advantageous embodiments and developments of the invention are specified in the rest of the claims.